Fate Tracing Reveals the Pericyte and Not Epithelial Origin of Myofibroblasts in Kidney Fibrosis

Renal Division, Department of Medicine, Brigham & Women's Hospital and Harvard Medical School, Boston, Massachusetts 02115, USA.
American Journal Of Pathology (Impact Factor: 4.6). 12/2009; 176(1):85-97. DOI: 10.2353/ajpath.2010.090517
Source: PubMed

ABSTRACT Understanding the origin of myofibroblasts in kidney is of great interest because these cells are responsible for scar formation in fibrotic kidney disease. Recent studies suggest epithelial cells are an important source of myofibroblasts through a process described as the epithelial-to-mesenchymal transition; however, confirmatory studies in vivo are lacking. To quantitatively assess the contribution of renal epithelial cells to myofibroblasts, we used Cre/Lox techniques to genetically label and fate map renal epithelia in models of kidney fibrosis. Genetically labeled primary proximal epithelial cells cultured in vitro from these mice readily induce markers of myofibroblasts after transforming growth factor beta(1) treatment. However, using either red fluorescent protein or beta-galactosidase as fate markers, we found no evidence that epithelial cells migrate outside of the tubular basement membrane and differentiate into interstitial myofibroblasts in vivo. Thus, although renal epithelial cells can acquire mesenchymal markers in vitro, they do not directly contribute to interstitial myofibroblast cells in vivo. Lineage analysis shows that during nephrogenesis, FoxD1-positive((+)) mesenchymal cells give rise to adult CD73(+), platelet derived growth factor receptor beta(+), smooth muscle actin-negative interstitial pericytes, and these FoxD1-derivative interstitial cells expand and differentiate into smooth muscle actin(+) myofibroblasts during fibrosis, accounting for a large majority of myofibroblasts. These data indicate that therapeutic strategies directly targeting pericyte differentiation in vivo may productively impact fibrotic kidney disease.

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Available from: Ben Humphreys, May 16, 2014
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    • "Each single color segment was uninterrupted by any single cell of another color, ruling out migration of other cells into the clonal region. In each time point (1, 2, 4, and 7 months), only epithelial cell types were in the clone, indicating that physiological epithelial-mesenchymal transformation (EMT) is not apparent within the kidney (Duffield and Humphreys, 2011; Duffield, 2010). These results are not consistent with interstitial mesenchymal cells contributing to renal epithelial repair (Humphreys et al., 2008, 2010) but are consistent with intrinsic renal epithelial cells that mediate tubulogenesis. "
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    ABSTRACT: The mechanism and magnitude by which the mammalian kidney generates and maintains its proximal tubules, distal tubules, and collecting ducts remain controversial. Here, we use long-term in vivo genetic lineage tracing and clonal analysis of individual cells from kidneys undergoing development, maintenance, and regeneration. We show that the adult mammalian kidney undergoes continuous tubulogenesis via expansions of fate-restricted clones. Kidneys recovering from damage undergo tubulogenesis through expansions of clones with segment-specific borders, and renal spheres developing in vitro from individual cells maintain distinct, segment-specific fates. Analysis of mice derived by transfer of color-marked embryonic stem cells (ESCs) into uncolored blastocysts demonstrates that nephrons are polyclonal, developing from expansions of singly fated clones. Finally, we show that adult renal clones are derived from Wnt-responsive precursors, and their tracing in vivo generates tubules that are segment specific. Collectively, these analyses demonstrate that fate-restricted precursors functioning as unipotent progenitors continuously maintain and self-preserve the mouse kidney throughout life.
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    • "S5A,B) or in adult mice (Supplemental Fig. S5C). We crossed Lox-TetOn-Lin28a/LIN28B mice with mice carrying FoxD1Cre (n = 10) to effect stromal cell-specific expression (Humphreys et al. 2010) and with mice carrying Cdh16Cre (n = 7) to effect UB cell-specific expression (Shao et al. 2002), but neither of these crossings reproduced the tumor phenotype. Interestingly, however, overexpression of LIN28B in stromal cells (FoxD1Cre) led to hydronephrosis in the adult kidney (Supplemental Fig. S5D), while no pathology was seen in the Cdh16Cre mice. "
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    • "Most components of the nephron, including the glomerulus, proximal tubule, loop of Henle, distal tubule, and connecting tubule, derive from a population of multipotent, self-renewing progenitor cells (Boyle et al., 2008; Kobayashi et al., 2008; Little and McMahon, 2012; Mugford et al., 2008), whereas the mesangial and endothelial cells of the glomerulus arise from different progenitor cells (Humphreys et al., 2010; Little and McMahon, 2012). The nephron progenitor cells (also known as cap mesenchyme [CM] cells) are a subset of the MM cells, which condense around the UB tips beginning at approximately embryonic day 11.5 (E11.5) in the mouse, shortly after the UB invades the MM and begins to branch. "
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